<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <link href="css/bootstrap.min.css" rel="stylesheet" type="text/css">
    <link href="css/base.css" rel="stylesheet" type="text/css">
    <style>
        select{width:100px;height:50px;border:solid 1px black;}
    </style>
</head>
<body>
<select id="year" onchange="changeDate()">
</select>
<select id="month" onchange="changeDate()"></select>
<select id="date"></select>
<script src="js/jquery-3.0.0.min.js"></script>
<script src="js/bootstrap.min.js"></script>
<script src="js/base.js"></script>
<script>

</script>
</body>
</html>